Thanks Chris, after doing some research, it looks like I'll need to upgrade my wire to 8 gauge.

My "Boom Boom" Bass Freak Kid Had dual 15's in a HUGE Box in his Ford Exolporer.He had dual 2000 watt amps !One for each woofer.He got a bigger alternator, DUAL Batterys, and Capacitors.18 Amps is considerable draw, do you run OFF a Marine Deep Cycle Battery Mike, or just leave Truck running ?

If I bought another battery same size and wired it parallel with my other one, would that be enough?

Maybe ?Deep Cycle Marine batterys are cheap here in Florida.I used two in Parallel for my dual shurflo's, back in the day.It has been MY experience that any 12 volt pump is a "Toy" compared to what we use.They may be "rated" at 7 gpm.but they just dont seem to spray like a diapragm pump does.Plus, they dont last either.I would rather see you get a Yamada NDP 15 FPS and an air compressor.It is a Poly Pump, but I used one, and rinsed it out and it lasted a year doing average 3 roofs a day, 5 days a week.The Kynar version is even better.It is up to you, but THINK it through good ?